1. Field of the Invention
The present invention relates to a high-pressure fuel supply assembly used in a cylinder-injected engine, for example.
2. Description of the Related Art
FIG. 6 is a block diagram showing a construction of a conventional high-pressure fuel supply assembly 100, FIG. 7 is a partially removed cross section of the high-pressure fuel supply assembly 100, FIG. 8 is a front elevation of the low-pressure damper 5 in FIG. 7, and FIG. 9 is a cross section of the high-pressure regulator 10 in FIG. 7.
This high-pressure fuel supply assembly 100 includes: a low-pressure damper 5 through which flows low-pressure fuel conveyed by a low-pressure fuel pump 2 within a fuel tank 1, the low-pressure damper 5 being connected to a low-pressure fuel intake passage 3; a high-pressure fuel pump 6 for pressurizing low-pressure fuel from the low-pressure damper 5 and discharging it into a high-pressure fuel discharge passage 7; a high-pressure damper 8 for absorbing surges in the high-pressure fuel flowing through the high-pressure fuel discharge passage 7; and a high-pressure regulator 10 for adjusting the pressure of the high-pressure fuel to a predetermined pressure, the high-pressure regulator 10 being disposed in a side passage 9 branching from the high-pressure fuel discharge passage 7.
Moreover, reference numeral 4 is a low-pressure regulator mounted in a passage branching from the low-pressure fuel intake passage 3, numeral 12 are filters, numeral 13 are check valves, numeral 14 is a drainage passage returning fuel from the high-pressure fuel pump 6 to the fuel tank 1, numeral 15 are delivery pipes connected to the high-pressure fuel discharge passage 7, and numeral 16 are fuel injection valves mounted on the delivery pipes 15.
The above low-pressure damper 5 is mounted in a first recess 50a in a casing 50. The low-pressure damper 5 includes: a cylindrical stainless-steel holder 51; a stainless-steel base 54 having a ball 53 disposed in a bore 52; and a stainless-steel bellows 55 disposed inside the holder 51.
The above high-pressure fuel pump 6 includes: a valve assembly 20 for opening and closing the low-pressure fuel intake passage 3 and the high-pressure fuel discharge passage 7; and a high-pressure fuel supply body 21 for pressurizing low-pressure fuel and discharging it into the high-pressure fuel discharge passage 7.
FIG. 10 is a cross section of the valve assembly 20, the valve assembly 20 being composed of: a first plate 22; a second plate 23; and a thin, flat valve main body 19 positioned between the first and second plates 22 and 23. A first fuel inlet 24 connected to the low-pressure fuel intake passage 3 and a first fuel outlet 25 connected to the high-pressure fuel discharge passage 7 are formed in the first plate 22, the inside dimensions of the first fuel outlet 25 being larger than the inside dimensions of the first fuel inlet 24. A second fuel inlet 26 having inside dimensions larger than those of the first fuel inlet 24 and a second fuel outlet 27 having inside dimensions smaller than those of the first fuel outlet 25 are formed in the second plate 23. The valve main body 19 is provided with: an intake-side tongue 28 interposed between the first fuel inlet 24 and the second fuel inlet 26; and a discharge-side tongue 29 interposed between the first fuel outlet 25 and the second fuel outlet 27.
The high-pressure fuel supply body 21 includes: an aluminum casing 50 housing the valve assembly 20 inside a second recess 50b; a cylindrical sleeve 30 housed in surface contact with the second plate 23 of the valve assembly 20; a piston 33 slidably inserted inside the sleeve 30 forming a fuel pressurization chamber 32 in cooperation with the sleeve 30; and a first spring 36 disposed between a recessed bottom surface 34 of the piston 33 and a holder 35, the spring 36 applying force to the piston 33 in a direction which expands the volume of the fuel pressurization chamber 32.
The high-pressure fuel supply body 21 also includes: a housing 37 fitted over the sleeve 30; a ring-shaped securing member 38 securing the valve assembly 20, the sleeve 30, and the housing 37 inside the second recess 50b of the casing 50 by fitting over the housing 37 and engaging the second recess 50b of the casing 50 by means of a male thread portion formed on an outer circumferential surface of the securing member 38; a stainless-steel bellows 40 disposed between the housing 37 and a receiving portion 39 secured to a tip portion of the piston 33; a second spring 41 compressed and disposed around the outside of the bellows 40 between the housing 37 and a holder 42; and a bracket 43 disposed to surround the second spring 41, the bracket 43 being secured to the casing 50 by a bolt (not shown).
The high-pressure fuel supply body 21 also includes: a tappet 44 slidably disposed in a slide bore 43a in an end portion of the bracket 43; a pin 45 rotatably suspended in the tappet 44; a bush 46 rotatably disposed on the pin 45; and a cam roller 47 rotatably disposed on the bush 46, the cam roller 47 contacting a cam (not shown) secured to a cam shaft (not shown), following the shape thereof, and reciprocating the piston 33.
The high-pressure regulator 10 is disposed inside a third recess 50c in the casing 50. The high-pressure regulator 10 includes: a valve 80 reciprocating axially; a holder 81 disposed opposite the valve 80; an adjusting screw 82 for determining the axial position of the holder 81, a tip of the screw contacting the holder 81; a spring 83 compressed and disposed between the valve 80 and the holder 81; a pipe 84 surrounding the holder 81 and a portion of the valve 80; a stainless-steel valve seat 85 formed with a passage 86 in which the valve 80 reciprocates; and a plate 87 forming a volume chamber 88 for damping the valve 80, the plate 87 being joined to the valve seat 85 by welding. Moreover, the valve seat 85 is secured inside the third recess 50c at the entrance to the third recess 50c by means of the pipe 84, and a securing thread 89 is engaged at a central portion by the adjusting screw 82 which moves inwards and outwards axially.
In a high-pressure fuel supply assembly 100 having the above construction, the piston 33 is reciprocated by the rotation of the cam secured to the cam shaft of an engine (not shown) by means of the cam roller 47, the bush 46, the pin 45, and the tappet 44.
When the piston 33 is descending (during the fuel intake stroke), the volume of the inside of the fuel pressurization chamber 32 increases and the pressure inside the fuel pressurization chamber 32 decreases, and when the pressure inside the fuel pressurization chamber 32 becomes lower than the pressure in the first fuel inlet 24, the intake-side tongue 28 of the valve main body 19 bends towards the second fuel inlet 26, allowing fuel in the low-pressure fuel supply passage 1 to flow through the first fuel inlet 24 into the fuel pressurization chamber 32.
When the piston 33 is ascending (during the fuel discharge stroke), the pressure inside the fuel pressurization chamber 32 increases, and when the pressure inside the fuel pressurization chamber 32 becomes greater than the pressure in the first fuel outlet 25, the discharge-side tongue 29 of the valve main body 19 bends towards the first fuel outlet 25, allowing fuel in the fuel pressurization chamber 32 to flow through the first fuel outlet 25 and the fuel discharge passage 7 into the high-pressure damper 8, where fuel pressure surges are absorbed. High-pressure fuel is then supplied to the check valve 13 and the delivery pipes 15, and thereafter supplied to the fuel injection valves 16, which inject fuel into each of the cylinders (not shown) of the engine.
Moreover, after the high-pressure fuel has left the check valve 13, it enters the high-pressure regulator 10 through an inlet 90, and enters the interior of the valve seat 85 through an entrance 91 in the valve seat 85. When, the pressure of the fuel is above a predetermined pressure, the valve 80 is moved in opposition to the elastic force of the spring 83 and is separated from the valve seat, some of the fuel flowing through an outlet 93 and an overflow port 94 into the drainage passage 92 and returning to the fuel tank. In other words, high-pressure fuel above the predetermined pressure is not supplied to the delivery pipes 15. This fuel pressure is set by adjusting the position of the holder 81 by moving the adjusting screw 82 inwards or outwards.
Furthermore, fuel leaking out from between the piston 33 and the sleeve 30 is returned to the fuel tank 1 through the inside of the bellows 40 and the drainage passage 14.
In a high-pressure fuel supply assembly 100 of the above construction, a low-pressure damper weld portion A is formed where the holder 51 of the low-pressure damper 5 contacts the base 54, and high-pressure fuel pump weld portions B and C are formed where the bellows 40 contacts the housing 37 and the receiving portion 39, respectively. A high-pressure regulator weld portion D is formed where the plate 87 contacts the valve seat 85. It is necessary to ensure a good seal and resistance to corrosion at these weld portions A, B, C, and D, and for that reason the holder 51, the base 54, the bellows 55, the housing 37, the receiving portion 39, the bellows 40, the plate 87, and the valve seat 85 are all made of stainless steel.
However, although stainless steel has good corrosion resistance, it is an expensive material and is difficult to process, and therefore one problem has been that manufacturing costs have been high.
Furthermore, FIG. 11 is an enlargement of the conventional low-pressure damper weld portion A, and because tensile forces arise in this weld portion A in the direction of the arrows E due to thermal contraction during welding, another problem has been that cracks form easily.